In the design of auxilliary equipment for use on aircraft engines, such as variable speed, constant frequency generators and hydraulic pumps, it has been the practice of engine designers to require separate lubrication systems for such auxilliary equipments. The reason for this requirement is that any contamination of the jet engine lubrication system could lead to catastrophic failure, and very expensive maintenance procedures on the engine itself.
Heretofore, it has been the practice of the industry to require separate lubricating systems for aircraft auxilliary equipments in order to provide absolute assurance that there will be no contamination of the engine oil when auxilliary equipments overheat, or fail during service use. This procedure, however, has required the use of a secondary cooling and lubricating system which necessarily requires additional weight and additional complexity in the layout of the engine compartment. Even with separate oil systems, there is the danger that the failure of one generator or pump will induce failure of other auxilliary equipment on the same supply system.
Heretofore, eutectic disconnect shafts such as that illustrated in U.S. Pat. No. 3,889,789 have been utilized to protect engines and auxilliary equipments in the event of failure and overheating. In these systems, a eutectic element is responsive to the surrounding heat and this eutectic element melts, permitting collapse of the element because of loss of lateral support for wires which pass through the element.
In the thermal fuze mechanical disconnect illustrated in the '789 patent, there is no provision for the flow of lubricating and cooling oil across the splines 26 which connect the drive shaft to the torque receiving means or pump drive shaft 24. In this arrangement, there is a hole 60 which communicates with the diametral bore 40 in which the thermal fuze is positioned. This allows some melted eutectic material to flow into the radial portion 42 of the cap 34. As can be seen in FIG. 2, the radial portion of cap 34 is also in direct communication with the area around the splines which connect the drive shaft to the torque receiving means. Therefore, the eutectic material is free to pass the area of the splines, and, if any engine lubricant is present, it will contaminate the engine lubricant and consequently endanger the operation of the entire engine.
Still further, as can be seen in FIGS. 1 and 2, there is a substantial space between the cap member 34 and the inner walls of the driven end of the drive shaft which carries the splines. This provides yet another means of escape of the melted eutectic material into the region of the splines.
It is desirable to utilize the engine lubrication oil for cooling of the generator and, at the same time, bring the oil only into contact with bearings and seals and tubes of the type encountered in the engine gearbox.